In Patent Documents 1 to 3, a forming method of an MOS interface is disclosed based on test results using a substrate having a (0001) Si plane. The channel mobility of an MOSFET having a channel formed on the (0001) Si plane thereof however does not become 10 cm2/Vs or greater.
In Patent Document 4, on the other hand, disclosed is a method of increasing the channel mobility in an MOS structure to 30 cm2/Vs or greater by subjecting an SiC semiconductor device using, for a channel, a plane a, that is, a (11-20) plane in the plane orientation of a crystal to hydrogen annealing or treatment in a wet atmosphere. More specifically, the channel mobility is improved by carrying out the hydrogen annealing or treatment in a wet atmosphere at a properly selected concentration or temperature.
[Patent Document 1] Japanese Patent No. 3443589
[Patent Document 2] Japanese Patent No. 3491050
[Patent Document 3] Japanese Patent No. 3525149
[Patent Document 4] Japanese Patent Laid-Open No. 2003-69012 corresponding to U.S. Pat. No. 6,764,963
The channel mobility obtained in the method disclosed in Patent Document 4 is still insufficient and a further improvement in the channel mobility is expected. The improvement in the channel mobility is expected not only when a (11-20) plane is used but also when another plane direction is used.
Thus, it is required for an SiC semiconductor device to improve channel mobility.